Enstatite, a magnesium silicate (MgSiO.sub.3), is a refractory chain silicate that exhibits a unique combination of properties: high strength and toughness combined with refractoriness and high creep resistance. The mineral undergoes a martensitic transformation from the orthorhombic phase, protoenstatite, to the monoclinic phase, clinoenstatite. This transformation develops polysynthetic twinning, which is responsible for an unusually high fracture toughness. Thus, enstatite is a transformation toughened material that has high use temperatures in the range of 1200.degree.-1500.degree. C.
Heretofore, essentially pure enstatite has not been available, since MgSiO.sub.3 is not a glass forming composition. Therefore, other glass formers and modifiers, such as ZrO.sub.2, Li.sub.2 O and BaO, need to be incorporated in order to melt a glass.
U.S. Pat. No. 4,687,749 (Beall) discloses a family of MgO-Al.sub.2 O.sub.3 -SiO.sub.2 glasses capable of being converted to glass-ceramics. In the glass-ceramic state, one or more polymorphs of enstatite constitute the primary crystal phase, along with various secondary phases. These secondary phases impart properties to the material that differ from those of pure enstatite.